IMO it really depends on what type/ style of riding you will be doing with the supermoto. If you want something to do basic lot stuff on and to learn circles and what not...wr250 is wicked because its light,buy brandnew,street legal and RM makes parts for them.

I feel that a blue plated crf450 or yzf450 are your best choices for being able to buy parts, stunt, dirt, fmx, fast to escape in the city streets and you can throw them on the ground all day and pick it back up and they keep going. It is a lot of bike to learn to stunt on but just depends on your riding skill.